Taurine as a Plant Growth Stimulator
Exogenous application of taurine has been reported to increase crop harvest, yield, and biomass (1). Applications of taurine by foliar spray, soil and roots application, and seed immersion increase crop production and seedling growth (1). Exogenous applications of taurine have also been shown to increase photosynthetic capacity of isolated plant cells (protoplasts and chloroplasts) (1). Increased taurine production in plants can enhance plant growth and development, yield, or tolerance to biotic and/or abiotic stresses. Increased yield, growth, or biomass may be a result of increased nitrogen flow, sensing, uptake, storage, transport or nitrogen use efficiency. Increased yield, growth or biomass may also be a result of increased carbon metabolism due to increased photosynthesis or increased carbohydrate metabolism by increased sucrose production and/or transport or increase biosynthesis or mobilization of starch, or oil. Increased yield, growth or biomass may also be associated with increased phosphorus uptake, transport or utilization. Increased yield, growth or biomass may also be associated with increased sulfur or sulfate uptake, transport or utilization. Increased yield, growth or biomass may also be associated with increased water uptake, transport, utilization or water-use-efficiency. Increased yield, growth or biomass may also be due to changes in the cell cycle modifications that improve growth rates and may increase early vigor and accelerate maturation leading to improved yield. Increased yield, growth or biomass may also be due to changes in the production of hormones or signaling molecules that regulate and improve plant growth and development leading to improvements in yield and biotic or abiotic stress tolerance. Increases in carbon, nitrogen, phosphorus, or sulfate flow, sensing, uptake, storage, transport or efficiency may improve seed quality for starch, oil or protein content. Increased yield, growth or biomass may also be a result of increased tolerance to abiotic stress such as changes in osmotic conditions, oxidative damage, drought, salt, cold, freezing, heat, UV light or light intensity. Increased yield, growth or biomass may also be a result of increased tolerance to biotic stress such as challenges, infection or insult from pests, pathogens, bacteria, microbes, viruses, viroids, microorganisms, invertebrates, insects, nematodes, or vertebrate. Increased yield, growth or biomass may be a result of increased tolerance to abiotic stresses such as changes in osmotic conditions or light intensity, oxidative damage, drought, salt, cold, freezing, heat, or UV radiation.
Taurine is an Essential Compound for Animals
Taurine is essential for human neonatal development (2) and plays an important role in brain development (3, 4). Taurine is involved in the modulation of intracellular calcium homeostasis (5, 6) and may balance glutamate activity, protecting neurons against glutamate excitotoxicity (7, 8). Taurine is also an osmoregulator (9). Taurine is essential for heart function (10), protects the integrity of hepatic tissue (11), and plays a role in photoprotection (12).
Taurine as a Pharmaceutical or Therapeutic
Taurine is used as a pharmaceutical and therapeutic. Taurine has been used in the treatment of cardiovascular diseases (13, 14), elevated blood pressure (15), seizure disorders (16), hepatic disorders (17), and alcoholism (18) and may be useful in the treatment of diabetes (19), Alzheimer's disease (20), and ocular disorders (21). Taurine has been shown to prevent obesity (22) and control cholesterol (23, 24). Taurine acts as an antioxidant and protects against toxicity of various substances (25-27). Taurine has been shown to prevent oxidative stress induced by exercise (28), and is used in energy drinks to improve performance (29). Taurine can also be used in topical applications to treat dermatological conditions (30).
Taurine as a Dietary Supplement
Taurine is biosynthesized in most animals and can be found in meat and seafood. Those who do not eat these foods regularly (e.g., vegetarians) or do not produce sufficient levels of taurine, e.g., cats (31), must acquire it through dietary supplement. Trout that are fed all-plant protein diets must acquire dietary taurine for normal growth (32).
Metabolic Pathways that Synthesize Taurine
With few exceptions (33, 34), taurine is found in plants only in low levels (35), and the metabolic pathway for taurine and hypotaurine has not yet been identified in plants. Several metabolic pathways that synthesize taurine and hypotaurine have been identified in animals and bacteria (FIG. 1). In animals, cysteine and oxygen are converted into 3-sulfinoalanine by cysteine dioxygenase (CDO). 3-sulfinoalanine is converted into hypotaurine by sulfinoalanine decarboxylase (SAD) or glutamate decarboxylase (GAD). Hypotaurine is converted into taurine either by the activity of hypotaurine dehydrogenase (HTDeHase) or by a spontaneous conversion. Cysteamine (2-aminoethanethiol) and oxygen are converted into hypotaurine by cysteamine dioxygenase (ADO), and hypotaurine is converted into taurine. Alternatively cysteine and sulfite are converted into cysteate and hydrogen sulfide by cysteine lyase (cysteine sulfite lyase or cysteine hydrogen-sulfide-lyase). Cysteate is converted into taurine by SAD or GAD. In bacteria, the compound 2-sulfoacetaldehyde is synthesized from acetyl phosphate and sulfite by sulfoacetaldehyde acetyltransferase (SA). Alanine and 2-sulfoacetaldehyde are converted into taurine and pyruvate by taurine-pyruvate aminotransferase (TPAT). In addition, sulfoacetaldehyde and ammonia (or ammonium) are converted into taurine and water in the presence of ferrocytochrome C by taurine dehydrogenase. Sulfite, aminoacetaldehyde, carbon dioxide and succinate are converted into taurine, 2-oxoglutarate and oxygen by taurine dioxygenase (TDO).